The proposed investigation is concerned with a test of the genetic developmental theory of aging at the level of the species, viz. Drosophila melanogaster. The goal of that investigation is to answer the following questions: to what extent are the large variations in life-span characteristic of a Drosophila population controlled by a specific set of genes? Which genes - major genes, minor genes, the so-called polygenes, with additive action and/or minor genes with epistatic action? Do these specific genes control life-span through a control of the developmental processes? It is propsed to answer these questions by measuring, in populations of Drosophila submitted to various genetic manipulations, simulataneously the variations in life-span and in traits related to the developmental processes, viz. growth-rate and mitotic division rate. Taking into account the results of some previous experiments made in our laboratory and attempting to increase life-span in Drosophila melanogaster by artificial selection, populations of Drosophila will be submitted to natural selection and to in- and cross-breeding. Furthermore, mutations of major genes affecting specific traits related to growth-rate will be analysed, in various environmental conditions, for the traits retained in this study. It is hoped that the measure of mitotic division rate in a holometabolous insect in which no mitotic division occurs after emergence will allow to bridge a gap between the study of cellular aging and of aging at the level of the organism. The potential usefulness of the proposed investigation is to give some ground or to disprove the genetic developmental theory of aging for which, in recent years, very few experimental data have been obtained.